This was on QI.

The enzymes in the dishwasher tablets need some dirt to glom onto, to be able to work. So pre-rinsing can make them less effective.

Tips I've learned that helped:

• use detergent powder instead of pods. It let's you experiment with different amounts and dial in the right amount for a run. Generic is fine, they all do about the same amount of work.
• Run your faucet till hot water comes out, it makes it so the pre-rinse has more ability to soften crud on the surface of the dishes.
• pre-rinsing the dishes isn't necessary for cleanliness, but scraping food bits off will mean your debris filter fills up slower so you don't have to do the gross task of emptying it as often.
• add detergent in the dip on the door. This gives the pre-wash yet again more ability to attack food bits on the first cycle.
• USE RINSE AID. I helps the dishes dry at the end of the wash.

Watch this if you think your dishwasher sucks.

As others have pointed out, it can be done albeit with more attention to detail than commercials imply. I wanted to mention the game changer for me was very reluctantly splurging for the expensive high-end tripple soap pods. These really made a big difference in my washer. I look for deals and buy them in bulk.

Use prewash detergent

Powder detergent only for both washes

Stack the dishwasher according to the manual

Don't leave your dishes for a week before putting them in the dishwasher

Do you run the water in your sink until it’s hot before turning on the dishwasher? Most kitchens are set up so they use the same water line, and starting with cold water if you don’t do it will make it clean worse.

Are you adding detergent to the pre rinse, or are you just throwing in one of those crappy packets?

I hate these commercials and I find it funny that they pay money to run them in my country where we have so much water we're practically drowning. We drink tap water and we leave the tap running for a quite some time just to get nice cold drinking water.

I could not give a damn about saving tap water. The dishes are rinsed before they go in the dishwasher.

This is a classic example of an American company assuming everyone else in the world think exactly like them, and subsequently completely fail with their marketing, at least in my part of the world.

Looks like there's something wrong with your dishwasher. I've had this effect once on one that couldn't heat up the water any more.

It depends a bit on what exactly the residue is you're talking about, but usually it's grease that wasn't properly picked up by the water, just redistributed among your dishes. That is usually because the dishwasher detergent did not properly activate, which in turn is usually because the water does not get hot enough. (Never mind some fats also just stay solid at room temperature.)

A properly working dishwasher does not leave any residue on your dishes.

When I was living in a trailer I used an organic pre wash solution that used no water and was 100% eco friendly to save water. Highly reccomend the heeler pre wash